SUBSIM Radio Room Forums - AI Radar = does it work at all

I wonder if ships did in fact opened fire upon just seeing a blip on a radar screen - in this way you can easily fire upon a, say, neutral fisherman or even a friendly. What were Rules of Engagement regarding radar contacts during the war? As I know from aviation sources even now a visual ID is often required on a radar contact before firing anything at it.
Moreover how precise were the radars of the day in the sense of spatial resolution or size of the target determination? I doubt that a battleship captain would order a full broadside on an unidentified radar contact which position and size are not known exactly - it is well known fact that main weapon ammunition can be: a) limited, b) very expensive (that is why BBs were given secondary weapons), and if you fire only secondary guns where is the guarantee that they will cause any damage (what if it is an enemy BB) while simultaneously breaking the element of surprise?
Even if we take the situation Hood vs. Bismark where the latter fired on radar range (as claimed by some authors it was the RF that helped to win) - it was not a situation where both did not see each other on the opposite both ship saw each other clearly, Bismark did not fire on an unidentified radar contact.
Returning to our situaton I suspect that while sailing in heavy fog and upon seeing a radar contact which had a small size an escort DD would establish an attack run to confirm the contact visualy and only upon visual identification would it attack. And if the submarine did not have a working RWR a DD on a high-speed collision course appearing less than a third a mile away meant death way more certain than just a random guns barrage fired on a general direction giving a warning that the U-boot was detected and must dive straight away.